Devices, for example of basket-like shape, which are accommodated in reactors and generally, also for reasons of design or strength, consist of materials with good thermal conductivity such as metal or metal alloys, for example steel, expand when the reactor is for example heated to operating temperature or heats up due to the heat of reaction and contract when the reactor cools.
If such devices contain readily displaceable, particulate, for example bulk packings of cylindrical or stellate catalyst particles, the differences in thermal expansion between the device and said packing result in the formation of indentations, often irregular and funnel-shaped, into which the particles trickle or subside, conventionally from the peripheral region of device.
This is unwanted since non-uniformity of the packing conventionally results in impaired characteristics, for example with regard to the catalytic behavior thereof. This is because, for example, the flow velocity of a gas is higher in the indentations in the peripheral region than in regions without any indentation, so the residence time of the gas in the peripheral region conventionally falls and moreover a smaller catalytic area is available to the reaction gas there, so resulting in lower levels of catalytic conversion in the peripheral region and overall.
The above-described disadvantages are encountered for example in methods for producing nitrogen oxides and/or nitric acid by oxidizing ammonia in the presence of a catalyst, for example a catalyst gauze containing noble metal. The oxidation products of ammonia are here conventionally passed through a bed of a particulate nitrous oxide decomposition catalyst which is conventionally located in a basket-like device. In said method, the above-stated funnel-shaped indentations in this bed of nitrous oxide decomposition catalyst for example result in reduced decomposition of the laughing gas in the peripheral region of the catalyst bed, which in turn conventionally results in higher nitrous oxide emissions from the production plant which are not desired.
WO 2004/005187 A1 (Yara International) describes a “burner basket” with metal walls and a perforated bottom plate which is located in an ammonia oxidation burner. The metal walls have a specific geometry in order to suppress non-uniformity of the catalyst bed. WO 2004/005187 A1 does not disclose a thermal insulation layer.
WO 03/011448 A1 (Johnson Matthey Plc) describes a fluid-permeable fixed bed on a perforated bottom which is surrounded by a wall. The wall has a specific geometry in order to suppress non-uniformity of the catalyst bed. WO 03/011448 A1 does not disclose a thermal insulation layer.